With increase in capacity of information processing in recent years, various information recording technologies have been developed. In particular, the surface recording density of an HDD using a magnetic recording technology is continuously increasing at an annual rate of approximately 100%. Recently, an information recording capacity exceeding 320 gigabytes/platter with a 2.5-inch diameter of a magnetic recording medium for use in an HDD or the like has been demanded, and in order to satisfy such a demand, an information recording density exceeding 500 gigabytes/square inch is required to be realized.
In order to achieve high recording density in a magnetic recording medium for use in an HDD or the like, a perpendicular magnetic recording type has been suggested in recent years. In a perpendicular magnetic recording medium used for the perpendicular magnetic recording type, an easy axis of magnetization of a granular magnetic layer (a magnetic layer having a granular structure) is adjusted so as to be oriented in a perpendicular direction with respect to a base surface. The perpendicular magnetic recording type is more suitable for increasing a recording density than a conventional in-plane magnetic recording type, since the perpendicular magnetic recording type can suppress a so-called thermal fluctuation phenomenon that a recording signal is lost due to the thermal stability of the recording signal is impaired by a superparamagnetic phenomenon.
As a perpendicular magnetic recording medium used for the perpendicular magnetic recording type, a magnetic recording medium where a backing layer, an orientation control layer, a magnetic recording layer, and a protective layer are stacked on a non-magnetic base plate has been suggested (for example, see Patent Document 1). In such a magnetic recording medium, the magnetic recording layer is constituted with use of a Co alloy material having a hexagonal close packed structure (hcp structure), and the orientation control layer is composed of an intermediate layer that improves the characteristics of the magnetic recording layer and a seed layer that adjusts the crystal orientations of the intermediate layer and the magnetic recording layer. The intermediate layer is deposited by sputtering using Ru or a Ru alloy having the hcp structure, and composed of a first intermediate layer (first ground layer) that is formed under a low-pressure condition, and a second intermediate layer (second ground layer) that is formed under a high-pressure condition.